I.M.P. are straight-up villain protagonists. Protagonist doesn't equal hero, they aren't even anti-heroes or heroes by proxy. They kill for a profession, they break laws and even explicitly pride how evil they are. Even if they have humanizing or redeeming moments, evil is a business for them. One would have to be crazy to consider I.M.P. good guys, especially when compared Charlie Magne and the other protagonists of Hazbin Hotel, who ARE heroes since have good intentions, as they want to save damned souls and redeem them.